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Date: Mon, 9 Jul 2012 22:06:22 +0800 From: Fengguang Wu <fengguang.wu@...el.com> To: Steven Rostedt <rostedt@...dmis.org> Cc: David Rientjes <rientjes@...gle.com>, Pekka Enberg <penberg@...nel.org>, JoonSoo Kim <js1304@...il.com>, Vegard Nossum <vegard.nossum@...il.com>, Christoph Lameter <cl@...ux.com>, Rus <rus@...nxsoft.com>, Ben Hutchings <ben@...adent.org.uk>, stable@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [patch] mm, slub: ensure irqs are enabled for kmemcheck On Mon, Jul 09, 2012 at 09:46:33AM -0400, Steven Rostedt wrote: > On Mon, 2012-07-09 at 03:36 -0700, David Rientjes wrote: > > kmemcheck_alloc_shadow() requires irqs to be enabled, so wait to disable > > them until after its called for __GFP_WAIT allocations. > > > > This fixes a warning for such allocations: > > > > WARNING: at kernel/lockdep.c:2739 lockdep_trace_alloc+0x14e/0x1c0() > > > > Cc: stable@...r.kernel.org [3.1+] > > Acked-by: Fengguang Wu <fengguang.wu@...el.com> > > Tested-by: Fengguang Wu <fengguang.wu@...el.com> > > Signed-off-by: David Rientjes <rientjes@...gle.com> > > --- > > mm/slub.c | 13 ++++++------- > > 1 file changed, 6 insertions(+), 7 deletions(-) > > > > diff --git a/mm/slub.c b/mm/slub.c > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -1314,13 +1314,7 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node) > > stat(s, ORDER_FALLBACK); > > } > > > > - if (flags & __GFP_WAIT) > > - local_irq_disable(); > > - > > - if (!page) > > - return NULL; > > - > > - if (kmemcheck_enabled > > + if (page && kmemcheck_enabled > > One micro-optimization nit... > > If kmemcheck_enabled is mostly false, and page is mostly true, wouldn't > it be better to swap the two? > > if (kmemcheck_enabled && page > > Then the first check would just short-circuit out and we don't do the > double check. I had the same gut feeling but at the time was not as conscious as you ;) Now I can dig out a similar optimization by Andrew Morton which also saves memory bytes: On Tue, Jun 19, 2012 at 03:00:14PM -0700, Andrew Morton wrote: : With my gcc and CONFIG_CGROUP_MEM_RES_CTLR=n (for gawd's sake can we : please rename this to CONFIG_MEMCG?), this: : : --- a/mm/vmscan.c~memcg-prevent-from-oom-with-too-many-dirty-pages-fix : +++ a/mm/vmscan.c : @@ -726,8 +726,8 @@ static unsigned long shrink_page_list(st : * writeback from reclaim and there is nothing else to : * reclaim. : */ : - if (PageReclaim(page) : - && may_enter_fs && !global_reclaim(sc)) : + if (!global_reclaim(sc) && PageReclaim(page) && : + may_enter_fs) : wait_on_page_writeback(page); : else { : nr_writeback++; : : : reduces vmscan.o's .text by 48 bytes(!). Because the compiler can : avoid generating any code for PageReclaim() and perhaps the : may_enter_fs test. Because global_reclaim() evaluates to constant : true. Do you think that's an improvement? Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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